<!DOCTYPE html>
<meta charset="utf-8">
<style>
html, body {
    margin: 0;
}
div {
    width: 32px;
    height: 32px;
    position: absolute;
    left: 0;
}
#a {
    background: green;
    top: 0;
}
#b {
    background: blue;
    top: 32px;
}
</style>
<div id=a></div>
<div id=b></div>


